Fuel delivery pipes have conventionally been known in which fuel such as gasoline is supplied to plural cylinders of the engine upon providing plural injection nozzles. The fuel delivery pipe injects the fuel introduced from a fuel tank out of the plural injection nozzles to the inside of a plurality of intake pipes or cylinders of the engine, mixes the fuel wit the air, and generates the engine output by burning the mixture gas.
The fuel delivery pipe, as described above, is for injecting the fuel supplied from the fuel tank via a supplying pipe out of the injection nozzle into the intake pipe or cylinder of the engine. A return type fuel delivery pipe exists in which having a circuit returning excessive fuel to the fuel tank with a pressure adjusting valve in a case where the supplied fuel is excessively supplied to the fuel delivery pipe. Moreover, a non-return type fuel delivery pipe, as different from the return type fuel delivery pipe, also exists in which having no circuit for returning the supplied fuel to the fuel tank.
The types for returning the fuel excessively supplied at the fuel delivery pipe to the fuel tank are advantageous in suppressing pulsation waves accompanying with fuel injections because the fuel amount in the fuel delivery pipe can be kept constant. However, the fuel supplied to the fuel delivery pipe disposed adjacently to the engine cylinder heated at a high temperature increases the temperature of the fuel, and the gasoline temperature in the fuel tank may be increased by returning the excessive fuel of the high temperature to the fuel tank. With this increased temperature, the gasoline may be gassed and unfavorably affect the environments adversely, so that the non-return type fuel delivery pipes have been proposed in which the excessive fuel is not returned to the fuel tank.
The non-return type fuel delivery pipe tends to generate large pulsation waves due to large pressure fractures, and the pulsation waves are generated much more than that in the return type fuel delivery pipe, because the non-return type fuel delivery pipe has no pipe for returning an excessive fuel to the fuel tank where the injection nozzles make injections to the intake pipes or cylinders.
This invention uses a fuel delivery pipe of a non-return type which otherwise tends to generate pulsation waves. In prior art, an interior of the fuel delivery pipe is locally, abruptly subject to a reduced pressure due to the fuel injection out of the injection nozzles into the intake pipes or cylinders of the engine, thereby generating pulsation waves (coarse and dense waves). This pulsation waves, after propagated at propagation rates of the respective pulsation waves in the fuel delivery pipe and the respective structural parts which constituting portions from connection pipes connecting to the fuel delivery pipe to the side of the fuel tank and through which the fuel is in communication, are returned reversely from the pressure adjusting valve in the fuel tank and propagated up to the fuel delivery pipe via the connection pipes. The fuel delivery pipe is formed with the plural injection nozzles, and the plural injection nozzles inject the fuel sequentially, thereby generating the pulsation waves.
The pulsation wave propagates at pulsation wave propagation rate corresponding to the respective structural parts through the system as doing reflections and transmissions according to changes in, e.g., the pulsation wave propagation rate and flowing speed at the boundaries among the structural parts through which the fuel communicates. The fuel delivery pipe ordinarily has a significantly larger flowing route cross section in comparison with the connection pipe or with the supplying pipe and has a large reflectance at a boundary plane at which the pulsation wave transmits from the fuel delivery pipe to the connection pipe and the supplying pipe. In a case where the fuel delivery pipe itself has a mechanism absorbing the pulsation wave with elastic transformation thereof, the propagation rate of the pulsation wave in the fuel delivery pipe becomes low due to significant differences in the elasticity thereof. The elastic transformation due to the pulsation wave can be neglected at the structural parts other than the fuel delivery pipe, and the propagation rate of the pulsation wave becomes an eigenvalue of the medium, or namely the fuel. Consequently, the reflectance at this boundary becomes larger. With this large reflectance, the pressure fluctuation in the fuel delivery pipe is absorbed very gently by the pressure adjusting valve in the fuel tank, and has a period characteristic to the system. The resonance phenomenon occurs when this period coincides to the injection period of the respective injection nozzles.
In a V-type engine, where the fuel delivery pipes are mounted with a pair thereof at each bank, the pulsation wave gently absorbed at the pressure adjusting valve in the fuel tank is made large at a component reciprocating between the fuel delivery pipe pair, and the pulsation wave has a characteristic period gentle as a whole since the reflectance at the boundary plane between the fuel delivery pipe and the connection pipe is large. Substantially in the same manner as above, the resonance phenomenon occurs when this period coincides to the injection period of the respective injection nozzles.
If the pulsation resonance point is generated out of the rotation speed region for the normal use of the engine, there would be no problem, but if the point occurs in the rotation speed region for the normal use of the engine, various disadvantages may be produced. It is to be noted that the rotation region of the engine in this specification means a desirable rotation speed region for the normal use of the engine.
That is, if the pulsation resonance point enters in the rotation region of the engine, the pressure in the fuel delivery pipe is abruptly reduced by the pulsation resonance, thereby generating a phenomenon that the fuel to be injected in the intake pipes or cylinders of the engine decreases. This makes the mixing rate of the fuel gas and the air different from the designed value, so that the exhaustion gas may be adversely affected, or that the designed power may not be pulled out. The pulsation resonance induces mechanical vibrations at the supplying pipe coupled to the side of the fuel tank, and is propagated as noises in the passenger room via clips that engage the supplying pipe to the bottom of the floor, so that the noises give the driver and the passengers uncomfortable feelings.
As conventional methods for reducing the various defects as described above caused by such a pulsation resonance and for suppressing problems caused by occurrences of the pulsation resonance, a pulsation dumper having inside a rubber diaphragm is arranged to the non-return type fuel delivery pipe to reduce the generated pulsation wave energy by absorption of the pulsation dumper, or the supplying pipe disposed below the floor extending from the fuel delivery pipe to the side of the fuel tank is secured with rubber made clips for absorbing vibrations or foamed resin made clips to reduce vibrations generated at the fuel delivery pipe or the supplying pipe extending up to the fuel pipe by absorption. These methods are relatively effective and have an effect to reduce the problems due to generation of the pulsation resonance.
Use of the pulsation dumper or clips for absorbing vibrations, however, though having an effect to reduce the problems due to occurrences of the pulsation resonance, cannot eliminate surely the problems. The pulsation dumper and the clip for absorbing vibrations are expensive, increase the number of the parts and the costs, and also raise new problems to ensure the installation space. Therefore, a fuel delivery pipe has been proposed in having a pulsation absorption function capable of absorbing the pulsation wave for the purpose of reducing the pulsation wave without using such a pulsation dumper or clips for absorbing vibrations and of transiting the generation of the pulsation resonance out of the low rotation region.
As the fuel delivery pipes having such an absorbing function of pulsation waves, known are the inventions in JP-A-2000-329030, JP-A-2000-320422, JP-A-2000-329031, JP-A-H11-37380, JP-A-H11-2164, and JP-A-S60-240867.
Those fuel delivery pipes having the absorbing function of pulsation waves have an effect to reduce the pulsation wave generated in accompany with the fuel injection. In a case where the fuel delivery pipes are used for the in-line type engine, the eigenvalue described above tends to be relatively low, and the pulsation resonance point frequently comes out of the low rotation speed region of the engine.
In an opposed type engine, such as a horizontal opposed type or a V-type engine, in which: banks having plural cylinders are disposed parallel; fuel delivery pipes are disposed in the banks having the plural cylinders; a pair of the fuel delivery pipes are coupled via a connection pipe; and a part of the connection pipe or one fuel delivery pipe is directly coupled to the side of the fuel tank via the supplying pipe, the pulsation resonance frequently enters in the use rotary region of the engine. Even in the in-line type engine, the pulsation resonance may enter in the use rotary region of the engine where the supplying pipe is so short in relation to the arrangement of the fuel tank.
With a six cylinder opposed type engine in which the fuel delivery pipe itself has a pulsation absorption mechanism, it was experimentally confirmed that the pulsation resonance phenomenon occurs around a region of 2,000 to 4,000 rpm. Because this rotation speed region is within the range of normal use of the engine, the fuel injection is affected as described above to deviate the mixing rate of the fuel and the air, thereby producing an unfavorable result from a viewpoint to cleaning of exhaustion gas, a result that the engine may be suffered from a lower output, or a result that noises are introduced into the passenger compartment in the automobile via the supplying pipes.
In a three cylinder in-line engine in which the fuel delivery pipe itself has a pulsation absorption mechanism and in which the supplying pipe has a length approximately half of the ordinary length, it was experimentally confirmed that the pulsation resonance phenomenon occurs around a region of 1,000 rpm. Similarly to the above example, substantially the same disadvantages may occur because the point is within the rotational speed region of normal use of the engine.
Those resonance phenomena occur, as described above, from coincidence between a slow characteristic period of a pulsation wave characteristic to a fuel supply system located between the fuel tank and the fuel delivery pipe and an injection period of the injection nozzle. The generation of the resonation phenomenon in the in-line engine is controlled by the characteristic period of the pulsation between the fuel delivery pipe and the pressure adjusting valve in the fuel tank. On the other hand, the generation of the resonation phenomenon in the opposed type engine is controlled by the eigenfrequency of the pulsation between the fuel delivery pipe pair. In an ordinary four cycle engine, the following relation is found between this period and the rotation speed of the engine.
 Engine rotational speed [rpm]=1/(characteristic period [sec])×60×(2/(nozzle number in bank))   [Formula 1]
The characteristic period may therefore be in a real use rotation region of the engine according to the number of the injection nozzles in the fuel delivery pipes.
A value analysis of the system is tried to find out what determines the characteristic period of the fuel supplying system. Where the propagation speeds of the pulsation waves in the respective structural components such as fuel delivery pipes, connection pipes, and supplying pipes in which the fuel for the system communicates, are previously sought, and where the value analysis of the wave equation is made in consideration of serial conditions relating to the flow rate and pressure to the boundary of the respective structural components, it was turned out that the characteristic period of the pulsation wave is controlled by the propagation speed of the pulsation wave in the fuel delivery pipes, the length of the fuel delivery pipes, and the fluid route cross-sectional area ratio of the fuel delivery pipe to the connection pipe or supplying pipe. In the in-line type engine, it was turned out that the length of the supplying pipe connecting the fuel delivery pipe and the pressure adjusting valve in the fuel tank does also affect greatly the characteristic period of the pulsation wave. In the opposed type engine having a pair of the fuel delivery pipes, the length of the connection pipe coupling between the pair of the fuel delivery pipes does also affect the characteristic period greatly.
The propagation speed of a pulsation wave in the above description is given as follows:α=[(1/ρ)/(1/Kf+1/Kw)]0.5  [Formula 2]
ρ: fuel density
Kf: fuel volume elastic modulus
Kw: volume elastic modulus of wall face of a fuel delivery pipe Kw=(ΔV/V)/ΔP
ΔP: pressure fluctuation
V: fuel delivery pipe volume
ΔV: volume fluctuation due to pressure fluctuation of the fuel delivery pipe
The volume elastic modulus Kw of the fuel delivery pipe can be sought by a value calculation in use of a finite element method or the like. It turned out that the volume elastic modulus Kw of the fuel delivery pipe of shapes shown in FIG. 4 and FIG. 5 was about 70 Mpa according to the value analysis. Where the fuel density ρ is 800 kg/m3, where the volume elastic modulus Kf of the fuel is 1 GPa, and where the volume elastic modulus Kw of the fuel delivery pipe is 70 Mpa, the propagation speed of the pulsation wave in the fuel delivery pipe is about 290 m/s. This value is confirmed approximately as correct from experiments. In a meanwhile, where the volume elastic modulus of wall face of a fuel delivery pipe is set infinite with the above fuel density and volume elastic modulus, the propagation speed of the pulsation wave is about 1120 m/s. Accordingly, the volume elastic modulus of wall face of the fuel delivery pipe is remarkably larger than the fluid volume elastic modulus in an annular pipe, and because the reciprocal number of the volume elastic modulus Kw of wall face of the fluid or fuel delivery pipe is placed on a side of the denominator of the formula of the propagation speed of the pulsation wave, the effect from the volume elastic modulus Kw of wall face of a fuel delivery pipe can be neglected mostly. In an ordinary pipe having such as a circle cross section, therefore, the propagation speed of the pulsation wave is about 1100 m/s, and it is confirmed experimentally.
For example, in a system for an opposed type engine in which the propagation speed of the pulsation wave of the fuel is 1000 m/s, in which the propagation speed of the pulsation wave in the fuel delivery pipe is 290 m/s, in which the length of the fuel delivery pipe pair is 300 mm, in which the length of the connection pipe is 200 mm, and in which the fluid route cross-sectional area ratio of the fuel delivery pipe to the connection pipe is 0.1, a value solution of the pressure fluctuation in a case where the pressure fluctuation occurs in one fuel delivery pipe is sought, and when the change in pressure difference as time goes between the banks is sought, it is turned out as a sine wave, whose characteristic period is 14.3 ms. When a situation of a V6-engine, namely having three injection nozzles at each bank, is supposed, the pulsation resonance point is about 2,800 rpm according to the above formula [Formula 1].
In a system for an in-line type engine in which the propagation speed of the pulsation wave of the fuel is 1100 m/s, in which the propagation speed of the pulsation wave in the fuel delivery pipe is 290 m/s, in which the length of the fuel delivery pipe pair is 300 mm, in which the length of the supplying pipe is 1000 mm, and in which the fluid route cross-sectional area ratio of the fuel delivery pipe to the connection pipe is 0.1, a value solution of the pressure fluctuation in a case where the pressure fluctuation occurs in the fuel delivery pipe is sought, and when the change in pressure difference in the fuel delivery pipe as time goes is sought, it is turned out as a sine wave as a matter of course, whose characteristic period is 39.1 ms. When a three-cylinder engine is supposed, the pulsation resonance point is about 1,000 rpm according to the above formula.